Anti-inflammatory Effects of Heme Oxygenase-1 Depend on Adenosine A2A- and A2B-Receptor Signaling in Acute Pulmonary Inflammation

The Pharmacological Effect of Hemin in Inflammatory-Related Diseases: A Systematic Review

BACKGROUND

Hemin is clinically used in acute attacks of porphyria; however, recent evidence has also highlighted its capability to stimulate the heme oxygenase enzyme, being associated with cytoprotective, antioxidant, and anti-inflammatory effects. Indeed, current preclinical evidence emphasizes the potential anti-inflammatory role of hemin through its use in animal models of disease. Nevertheless, there is no consensus about the underlying mechanism(s) and the most optimal therapeutic regimens. Therefore, this review aims to summarize, analyze, and discuss the current preclinical evidence concerning the pharmacological effect of hemin.

METHODS

Following the application of the search expression and the retrieval of the articles, only nonclinical studies in vivo written in English were considered, where the potential anti-inflammatory effect of hemin was evaluated.

RESULTS

Forty-nine articles were included according to the eligibility criteria established. The results obtained show the preference of using 30 to 50 mg/kg of hemin, administered intraperitoneally, in both acute and chronic contexts. This drug demonstrates significant anti-inflammatory and antioxidant activities considering its capacity for reducing the expression of proinflammatory and oxidative markers.

CONCLUSIONS

This review highlighted the significant anti-inflammatory and antioxidant effects of hemin, providing a clearer vision for the medical community about the use of this drug in several human diseases.

The Triterpenoid Nrf2 Activator, CDDO-Me, Decreases Neutrophil Senescence in a Murine Model of Joint Damage

The synthetic 2-cyano-3,12-dioxo-oleana-1,9(11)-dien-28-oic acid methyl ester (CDDO-Me) is a potent activator of the erythroid 2-p45-derived factor 2, Nrf2, a leucine-zipper regulator of the antioxidant response. Herein, we investigated the effect of CDDO-Me on neutrophil function in a murine model of joint damage. Collagenase-induced osteoarthritis (CIOA) was initiated by the intra-articular injection of collagenase in the knee-joint cavity of Balb/c mice. CDDO-Me was administrated intra-articularly twice a week starting at day 7 post-CIOA, and its effect was evaluated at day 14. Neutrophils in blood and bone marrow (BM), cell apoptosis, necrosis, expression of C-X-C chemokine receptor 4 (CXCR4), beta-galactosidase (β-Gal), and Nrf2 levels were measured by flow cytometry. In vitro, CDDO-Me promoted cell survival, reduced cell necrosis, and increased Nrf2 levels by 1.6 times. It decreased surface CXCR4 expression and reduced the frequency of senescent β-Gal+CXCR4+ neutrophils by three times. In vivo, the degree of knee-joint damage in CIOA was correlated with upregulated CXCR4 on CD11b+ neutrophils. CDDO-Me improved the disease histological score, increased the levels of Nrf2, and downregulated surface CXCR4 on mature BM cells. Our data suggest that CDDO-Me may act as a potent regulator of neutrophil senescence during the progression of knee-joint damage.

Heme, Heme Oxygenase-1, Statins, and SARS-CoV-2

Heme, a metalloporphyrin, or more specifically, a tetrapyrrole containing ferrous iron, is an ancient molecule [...]

Sevoflurane Dampens Acute Pulmonary Inflammation via the Adenosine Receptor A2B and Heme Oxygenase-1

Acute respiratory distress syndrome is a life-threatening disease associated with high mortality. The adenosine receptor A2B (Adora2b) provides anti-inflammatory effects, which are also associated with the intracellular enzyme heme oxygenase-1 (HO-1). Our study determined the mechanism of sevoflurane’s protective properties and investigated the link between sevoflurane and the impact of a functional Adora2b via HO-1 modulation during lipopolysaccharide (LPS)-induced lung injury. We examined the LPS-induced infiltration of polymorphonuclear neutrophils (PMNs) into the lung tissue and protein extravasation in wild-type and Adora2b−/− animals. We generated chimeric animals, to identify the impact of sevoflurane on Adora2b of hematopoietic and non-hematopoietic cells. Sevoflurane decreased the LPS-induced PMN-infiltration and diminished the edema formation in wild-type mice. Reduced PMN counts after sevoflurane treatment were detected only in chimeric mice, which expressed Adora2b exclusively on leukocytes. The Adora2b on hematopoietic and non-hematopoietic cells was required to improve the permeability after sevoflurane inhalation. Further, sevoflurane increased the protective effects of HO-1 modulation on PMN migration and microvascular permeability. These protective effects were abrogated by specific HO-1 inhibition. In conclusion, our data revealed new insights into the protective mechanisms of sevoflurane application during acute pulmonary inflammation and the link between sevoflurane and Adora2b, and HO-1 signaling, respectively.

The Impact of Hypoxia in Early Pregnancy on Placental Cells

Oxygen levels in the placental microenvironment throughout gestation are not constant, with severe hypoxic conditions present during the first trimester. This hypoxic phase overlaps with the most critical stages of placental development, i.e., blastocyst implantation, cytotrophoblast invasion, and spiral artery remodeling initiation. Dysregulation of any of these steps in early gestation can result in pregnancy loss and/or adverse pregnancy outcomes. Hypoxia has been shown to regulate not only the self-renewal, proliferation, and differentiation of trophoblast stem cells and progenitor cells, but also the recruitment, phenotype, and function of maternal immune cells. In this review, we will summarize how oxygen levels in early placental development determine the survival, fate, and function of several important cell types, e.g., trophoblast stem cells, extravillous trophoblasts, syncytiotrophoblasts, uterine natural killer cells, Hofbauer cells, and decidual macrophages. We will also discuss the cellular mechanisms used to cope with low oxygen tensions, such as the induction of hypoxia-inducible factor (HIF) or mammalian target of rapamycin (mTOR) signals, regulation of the metabolic pathway, and adaptation to autophagy. Understanding the beneficial roles of hypoxia in early placental development will provide insights into the root cause(s) of some pregnancy disorders, such as spontaneous abortion, preeclampsia, and intrauterine growth restriction.

Adenosine and Inflammation: Here, There and Everywhere

Adenosine is a ubiquitous endogenous modulator with the main function of maintaining cellular and tissue homeostasis in pathological and stress conditions. It exerts its effect through the interaction with four G protein-coupled receptor (GPCR) subtypes referred as A1, A2A, A2B, and A3 adenosine receptors (ARs), each of which has a unique pharmacological profile and tissue distribution. Adenosine is a potent modulator of inflammation, and for this reason the adenosinergic system represents an excellent pharmacological target for the myriad of diseases in which inflammation represents a cause, a pathogenetic mechanism, a consequence, a manifestation, or a protective factor. The omnipresence of ARs in every cell of the immune system as well as in almost all cells in the body represents both an opportunity and an obstacle to the clinical use of AR ligands. This review offers an overview of the cardinal role of adenosine in the modulation of inflammation, showing how the stimulation or blocking of its receptors or agents capable of regulating its extracellular concentration can represent promising therapeutic strategies for the treatment of chronic inflammatory pathologies, neurodegenerative diseases, and cancer.

Co-inhibition of CD73 and ADORA2B Improves Long-Term Cigarette Smoke Induced Lung Injury

Adenosine (ADO) involvement in lung injury depends on the activation of its receptors. The ADO A_2A receptor (ADORA2A) and A_2B receptor (ADORA2B) are best described to have both tissue-protective and tissue-destructive processes. However, no approach has been effective in delineating the mechanism(s) involved with ADO shifting from its tissue-protective to tissue-destructive properties in chronic airway injury. Using cigarette smoke (CS) as our model of injury, we chronically exposed Nuli-1 cells to 5% CS extract (CSE) for 3 years establishing a long-term CSE exposure model (LTC). We found significant morphological changes, decreased proliferation, and migration resulting in impaired airway wound closure in LTC. Further investigations showed that long-term CSE exposure upregulates CD73 and ADORA2B expression, increases ADO production, inhibits PKC alpha activity and p-ERK signaling pathway. Knocking down ADORA2B and/or CD73 in LTC activates PKC alpha and increases p-ERK signaling. Knocking down both showed better improvement in wound repair than either alone. In vivo experiments also showed that double knockout CD73 and ADORA2B remarkably improved CS-induced lung injury by activating PKC alpha, reducing the inflammatory cell number in bronchoalveolar lavage fluid and the production of inflammatory mediator IL-6, inhibiting the fibrosis-like lesions and decreasing collagen deposition surrounding bronchioles. Collectively, long-term CSE exposure upregulates CD73 expression and increases ADO production, which promotes low affinity ADORA2B activation and subsequent diminution of PKC alpha activity and ERK signaling pathway, and inhibition of airway wound repair. Moreover, the data suggesting ADORA2B and CD73 as potential therapeutic targets may be more efficacious in improving chronic CS lung diseases and impaired wound repair.

Inhibition of CXCR4 and CXCR7 Is Protective in Acute Peritoneal Inflammation

Our previous studies revealed a pivotal role of the chemokine stromal cell-derived factor (SDF)-1 and its receptors CXCR4 and CXCR7 on migratory behavior of polymorphonuclear granulocytes (PMNs) in pulmonary inflammation. Thereby, the SDF-1-CXCR4/CXCR7-axis was linked with adenosine signaling. However, the role of the SDF-1 receptors CXCR4 and CXCR7 in acute inflammatory peritonitis and peritonitis-related sepsis still remained unknown. The presented study provides new insight on the mechanism of a selective inhibition of CXCR4 (AMD3100) and CXCR7 (CCX771) in two models of peritonitis and peritonitis-related sepsis by injection of zymosan and fecal solution. We observed an increased expression of SDF-1, CXCR4, and CXCR7 in peritoneal tissue and various organs during acute inflammatory peritonitis. Selective inhibition of CXCR4 and CXCR7 reduced PMN accumulation in the peritoneal fluid and infiltration of neutrophils in lung and liver tissue in both models. Both inhibitors had no anti-inflammatory effects in A_2B knockout animals (A_2B–/–). AMD3100 and CCX771 treatment reduced capillary leakage and increased formation of tight junctions as a marker for microvascular permeability in wild type animals. In contrast, both inhibitors failed to improve capillary leakage in A_2B–/– animals, highlighting the impact of the A_2B-receptor in SDF-1 mediated signaling. After inflammation, the CXCR4 and CXCR7 antagonist induced an enhanced expression of the protective A_2B adenosine receptor and an increased activation of cAMP (cyclic adenosine mono phosphate) response element-binding protein (CREB), as downstream signaling pathway of A_2B. The CXCR4- and CXCR7-inhibitor reduced the release of cytokines in wild type animals via decreased intracellular phosphorylation of ERK and NFκB p65. In vitro, CXCR4 and CXCR7 antagonism diminished the chemokine release of human cells and increased cellular integrity by enhancing the expression of tight junctions. These protective effects were linked with functional A_2B-receptor signaling, confirming our in vivo data. In conclusion, our study revealed new protective aspects of the pharmacological modulation of the SDF-1-CXCR4/CXCR7-axis during acute peritoneal inflammation in terms of the two hallmarks PMN migration and barrier integrity. Both anti-inflammatory effects were linked with functional adenosine A_2B-receptor signaling.

New Insights into the Nrf-2/HO-1 Signaling Axis and Its Application in Pediatric Respiratory Diseases

Respiratory diseases are one of the most common pediatric diseases in clinical practice. Their pathogenesis, diagnosis, and treatment are thus worthy of further investigation. The nuclear factor erythroid 2-related factor 2/heme oxygenase 1 (Nrf2/HO-1) signaling axis is a multiple organ protection chain that protects against oxidative stress injury. This signaling axis regulates anti-inflammation and antioxidation by regulating calcium ions, mitochondrial oxidative stress, autophagy, ferroptosis, pyroptosis, apoptosis, alkaliptosis, and clockophagy. This review presents an overview of the role of the Nrf2/HO-1 signaling axis in the pathogenesis of pediatric respiratory diseases and the latest research progress on this subject. Overall, the Nrf2/HO-1 signaling axis has an important clinical value in pediatric respiratory diseases, and its protective effect needs further exploration.

CD73-dependent adenosine dampens interleukin-1β-induced CXCL8 production in gingival fibroblasts: Association with heme oxygenase-1 and adenosine monophosphate-activated protein kinase

BACKGROUND

During inflammation, stressed or infected cells can release adenosine triphosphate (ATP) to the extracellular medium, which can be hydrolyzed to adenosine by ectonucleotidases such as ectonucleoside triphosphate diphosphohydrolase 1 (CD39) and 5'-nucleotidase (CD73). The role of CD73 in the modulation of cytokine release by human gingival fibroblasts (HGFs) remains underexplored. Here, we investigated whether CD73-mediated hydrolysis of extracellular ATP (eATP) could affect interleukin (IL)-1β-induced CXCL8 secretion.

METHODS

The levels of mRNA expression of adenosine receptors, CD39 and CD73 of periodontitis samples were retrieved from a public database. Moreover, HGF mRNA levels were measured by quantitative reverse transcription-polymerase chain reaction (RT-qPCR) after 3, 6, or 24 hours of IL-1β stimulation. IL-1β-induced CXCL8 protein levels were measured after pretreatment with 100-µM eATP in the presence or absence of CD73 inhibitor. The effect of eATP degradation to adenosine on CXCL8 levels was investigated using agonist and antagonist of adenosine receptors.

RESULTS

Levels of CD39, CD73, and adenosine receptor mRNA were differentially modulated by IL-1β. ATP pretreatment impaired IL-1β-induced CXCL8 secretion and required activation of heme oxygenase-1 (HO-1) and phosphorylated adenosine monophosphate-activated protein kinase (pAMPK). The inhibition of CD73 or the inhibition of adenosine receptors abrogated the ATP effect on CXCL8 secretion.

CONCLUSIONS

CD73-generated adenosine dampens IL-1β-induced CXCL8 in HGFs and involves HO-1 and pAMPK signaling. These results imply that CD73 is a negative regulator of the inflammatory microenvironment, suggesting that this ectoenzyme could be involved in the generation of deficient CXCL8 gradient in chronic inflammation.

HO-1 and CD39: It Takes Two to Protect the Realm

Cellular protective mechanisms exist to ensure survival of the cells and are a fundamental feature of all cells that is necessary for adapting to changes in the environment. Indeed, evolution has ensured that each cell is equipped with multiple overlapping families of genes that safeguard against pathogens, injury, stress, and dysfunctional metabolic processes. Two of the better-known enzymatic systems, conserved through all species, include the heme oxygenases (HO-1/HO-2), and the ectonucleotidases (CD39/73). Each of these systems generates critical bioactive products that regulate the cellular response to a stressor. Absence of these molecules results in the cell being extremely predisposed to collapse and, in most cases, results in the death of the cell. Recent reports have begun to link these two metabolic pathways, and what were once exclusively stand-alone are now being found to be intimately interrelated and do so through their innate ability to generate bioactive products including adenosine, carbon monoxide, and bilirubin. These simple small molecules elicit profound cellular physiologic responses that impact a number of innate immune responses, and participate in the regulation of inflammation and tissue repair. Collectively these enzymes are linked not only because of the mitochondria being the source of their substrates, but perhaps more importantly, because of the impact of their products on specific cellular responses. This review will provide a synopsis of the current state of the field regarding how these systems are linked and how they are now being leveraged as therapeutic modalities in the clinic.

Pro-inflammatory Effect of Downregulated CD73 Expression in EAE Astrocytes

CD73, an ectonucleotidase, participates in the regulation of immune responses by controlling the conversion of extracellular AMP to adenosine. In this study, we investigated whether any type of brain cells, especially neuroglia cells, exhibit altered CD73 expression, localization or activity upon experimental autoimmune uveitis (EAU) induction and whether altered CD73 manipulates the activation of effector T cells that interact with such cell types. First, the amount of cell membrane-exposed CD73 was detected by flow cytometry in various types of brain cells collected from either naïve or EAE mice. Compared to that in astrocytes from naïve control mice, the amount of membrane-bound CD73 was significantly decreased in astrocytes from EAE mice, while no significant differences were detected in other cell types. Thereafter, wild-type and CD73-/- astrocytes were used to study whether CD73 influences the function of inflammatory astrocytes, such as the production of cytokines/chemokines and the activation of effector T cells that interact with astrocytes. The results indicated that the addition of exogenous AMP significantly inhibited cytokine/chemokine production by wild type astrocytes but had no effect on CD73-/- astrocytes and that the effect of AMP was almost completely blocked by the addition of either a CD73 inhibitor (APCP) or an adenosine receptor A1 subtype (ARA1) antagonist (DPCPX). Although the addition of AMP did not affect CD73-/- astrocytes, the addition of adenosine successfully inhibited their cytokine/chemokine production. The antigen-specific interaction of astrocytes with invading CD4 cells caused CD73 downregulation in astrocytes from mice that underwent EAE induction. Collectively, our findings support the conclusion that, upon EAE induction, likely due to an interaction with invading CD4+ cells, astrocytes lose most of their membrane-localized CD73; this inhibits the generation of adenosine in the local microenvironment. As adenosine has anti-inflammatory effects on astrocytes and CNS-infiltrating effector T cells in EAE, the downregulation of CD73 in astrocytes may be considered a pro-inflammatory process for facilitating the pathogenesis of EAE.

Alternate and Additional Functions of Erythrocyte Hemoglobin

The review discusses pleiotropic effects of erythrocytic hemoglobin (Hb) and their significance for human health. Hemoglobin is mostly known as an oxygen carrier, but its biochemical functions are not limited to this. The following aspects of Hb functioning are examined: (i) catalytic functions of the heme component (nitrite reductase, NO dioxygenase, monooxygenase, alkylhydroperoxidase) and of the apoprotein (esterase, lipoxygenase); (ii) participation in nitric oxide metabolism; (iii) formation of membrane-bound Hb and its role in the regulation of erythrocyte metabolism; (iv) physiological functions of Hb catabolic products (iron, CO, bilirubin, peptides). Special attention is given to Hb participation in signal transduction in erythrocytes. The relationships between various erythrocyte metabolic parameters, such as oxygen status, ATP formation, pH regulation, redox balance, and state of the cytoskeleton are discussed with regard to Hb. Hb polyfunctionality can be considered as a manifestation of the principle of biochemical economy.

Adenosine from a biologic source regulates neutrophil extracellular traps (NETs)

Neutrophil extracellular traps (NETs) are implicated in autoimmune, thrombotic, malignant, and inflammatory diseases; however, little is known of their endogenous regulation under basal conditions. Inflammatory effects of neutrophils are modulated by extracellular purines such as adenosine (ADO) that is inhibitory or ATP that generally up-regulates effector functions. In order to evaluate the effects of ADO on NETs, human neutrophils were isolated from peripheral venous blood from healthy donors and stimulated to make NETs. Treatment with ADO inhibited NET production as quantified by 2 methods: SYTOX green fluorescence and human neutrophil elastase (HNE)-DNA ELISA assay. Specific ADO receptor agonist and antagonist were tested for their effects on NET production. The ADO _2A receptor (A_2A R) agonist CSG21680 inhibited NETs to a similar degree as ADO, whereas the A_2A R antagonist ZM241385 prevented ADO's NET-inhibitory effects. Additionally, CD73 is a membrane bound ectonucleotidase expressed on mesenchymal stromal cells (MSCs) that allows manipulation of extracellular purines in tissues such as bone marrow. The effects of MSCs on NET formation were evaluated in coculture. MSCs reduced NET formation in a CD73-dependent manner. These results imply that extracellular purine balance may locally regulate NETosis and may be actively modulated by stromal cells to maintain tissue homeostasis.

Adenosine activates Gαs proteins and inhibits C3a-induced activation of human mast cells

Anaphylatoxin C3a and adenosine receptors (AR) are implicated in the inflammatory process associated with allergic rhinitis and asthma by modifying mast cell (MC) responses. Possible interactions between these G-protein coupled receptor (GPCR) pathways in MCs have not yet been demonstrated. LAD2 human MC were stimulated with C3a in the presence or absence of AR agonists and antagonists and their adhesion, chemotaxis and mediator release were measured. The pan-specific AR agonist, 5'-N-Ethylcarboxamidoadenosine (NECA) inhibited C3a-induced LAD2 cell migration, adhesion, degranulation, production of CCL2, and ERK1/2 phosphorylation. The selective A_2A receptor agonist CGS 21680 inhibited C3a-mediated degranulation, while the A_2B and A₃ receptor agonists BAY 60-6583 and IB-MECA, respectively, had no effect. Moreover, an A_2A receptor antagonist SCH 58261 blocked the inhibitory effect of NECA on C3a-induced degranulation, suggesting that inhibition of degranulation was mediated through the A_2A receptor. NECA increased intracellular cAMP in C3a-activated mast cells, suggesting that Gα_s protein signals are required for adenosine-induced inhibition of C3a-mediated human mast cell activation. The adenylyl cyclase inhibitor SQ 22536 attenuated the inhibitory effect of NECA on C3a-activated degranulation, and the A_2A agonist CSG 21680 potentiated the inhibition of mast cell activation mediated by the A_2A receptor. Our results suggest that adenosine inhibits C3a-mediated activation of human mast cells, possibly through a Gα_s protein-dependent pathway.

Migration and invasion in B16-F10 mouse melanoma cells are regulated by Nrf2 inhibition during treatment with ionizing radiation

Nuclear factor erythroid 2-related factor 2 (Nrf2) serves a critical role in carcinogenesis. The present study examined the effect of Nrf2 on the proliferation and invasion of melanoma cells that were treated with ionizing radiation. B16-F10 mouse melanoma cells were exposed to various doses of ionizing radiation for different time periods. Small interfering (si)RNAs targeting Nrf2 were transfected into B16-F10 cells, and cell proliferation, invasion and apoptosis were detected by Transwell, MTT or western blot assays. The expression of Nrf2 and its downstream heme oxygenase 1 (HO-1) was analyzed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting. HO-1 activity was also examined. Ionizing radiation stimulated Nrf2 expression, increased caspase-3 expression, and reduced the viability, migration and invasion of B16-F10 mouse melanoma cells. Transfection with Nrf2 siRNA was able to inhibit Nrf2 and HO-1 expression in B16-F10 mouse melanoma cells that were treated by ionizing radiation. Inhibition of Nrf2 further reduced cell viability, invasion and migration, and elevated caspase-3 expression in B16-F10 mice melanoma cells that were treated by ionizing radiation. In summary, treatment with ionizing radiation was able to stimulate Nrf2 expression and regulate cell viability, invasion and migration of B16-F10 cells. A combination of Nrf2 knockdown and ionizing radiation treatment exerted a synergistic effect on migration, invasion and apoptosis in B16-F10 murine melanoma cells.